Getter for electron discharge devices



April 1, 1941.

R B. VANDEGRIFT GETTER FOR ELECTRON DISCHARGE DEVICES Filed Feb. 29,1940 mummy, I'l HI! ROLAND B. VANDEGR/FT A TTORNE Y.

Patented Apr. 1, 1941 i UNITED STATES PATENT OFFICE GETTER FOR ELECTRONDISCHARGE DEVICES Roland B. Vandegrift, North Arlington, N. J., assignorto Radio Corporation of America, a corporation of Delaware ApplicationFebruary 29, 1940, Serial No. 321,414

4 Claims. (Cl. 250--27.5)

My invention relates to electron discharge devices, particularly togetters and means for vaporizing active metals in such devices.

Getter materials are commonly vaporized in the similar in constructionto the control grid comprising circularly arranged parallel rods joinedat their upper ends to a shielding cap l3 and fastened at their lowerends to the small end of the metal cone M, which is carried on theheader. The metal cone and the metal header effectively enclose andshield the input electrodes and leadin conductors from the electrostaticinfluence of the anode.

Getter material is carried on a resistance heating element l5 shown inthis tube as a grooved ribbon which is electrically connected at itsends to the two control grid lead-in conductors. In large tubes theheating element should comprise,

permanently connected between electrically sepaas shown, two or moreribbons connected in rate and insulated electrodes, at least one andparallel for carrying larger quantities of getter sometimes both of thegetter lead-ins must commaterial. The ribbons are supported upon metalprise conductors in addition to the electrode leadstraps I6 spot weldedto the getter ribbons and to in conductors. Additional lead-ins howeverinthe grid lead-ins at a point on the lead-ins near crease manufacturingcosts and in some tubes th l n hin have f n th t he tter seriouslycomplicate the design of the tubes. ribbons can be heated and the activemetals of A principal object of my invention is electron thegettervaporized by direct resistance heating, discharge devices with improvedmeans for elecalthough there is an apparent short circuit tricallyvaporizing getter material in the device. through the grid structureincluding the lower A more specific object of my invention is means gridco T0 t er ends of the d l for resistance heating a getter from anexternal in conductors are clamped the ends of a loop I] electricalsource without increasing the number of wire. Coupled to the loop is theoutput of a of lead-in conductors in the envelope. high frequency sourceof power Hi. It has been The characteristic features of my invention arefound that by raising the frequency of the high defined in the appendedclaims and one embodifrequency source to some value of moderate wavementthereof is described in the following specification and shown in theaccompanying drawing in which Figure 1 is a sectional view of a radiotube showing my improved getter.

The particular radio tube chosen for illustrating my invention and shownin the drawing comprises a transmitting tube for shortwave operation.The envelope of the tube is principally of metal and comprises acup-shaped anode I sealed along its rim by glass bulb 2 to a metalheader 3. High voltage bushings 4 hermetically seal the lead-inconductors in the metal header. The spiraled cathode 5 is steadied by acentral support rod 6, the lower end of which is omitted for clarity,and is surrounded by a tubular control grid 1 comprising a number ofparallel rods or wires held at their lower ends by metal rings 8 andguided at their upper ends by spacer 9. The grid is supported upon tworigid lead-in conductors I0 and II joined at their inner ends to thelower metal ring 8. The two lead-in conductors l0 and II for the gridhave been found necessary to reduce grid lead-in inductance in the tubewhen operated at ultra high frequencies.

The screen grid l2 in this particular tube is length, sufilcient currentcan be made to flow through the getter ribbon to raise it to flashingtemperature without overheating the grid dollar. In one tube in whichthe getter was spaced below the lower grid collar about thirtymillimeters, the getter could be easily flashed even though theresistance of the lower grid collar was much less than the resistance ofthe getter ribbon, I believe that the division of the high frequencycurrent through the higher resistance path of the getter ribbon isbecause of the lower total reactance of the ribbon path. The areas ofthe plane enclosed by the circuit including the getter and the lead-inconductors is less than the area of the circuit including the gridcollar. Since the inductance of a loop at high frequencies isapproximately proportional to the area of a plane surrounded by theloop, it is possible to increase the frequency of the electrical sourceto a value where the principal portion of the current will flow throughthe getter ribbon even though its ohmic resistance may be higher thanthe parallel grid collar path. The frequency .of the source usedaccordingly is a matter of choice determined by the relative areas ofthe two parallel loops and by the resistance of the two parallel paths.In a tube of the type shown a current timed to a frequency of aboutthree hundred kilocycles per second was suflicient to flash the getteralthough the getter was spaced below -the grid collar only about thirtymillimeters.

My improved electron discharge device comprises a resistance heatedgetter that may be flashed from an external source of power withoutincreasing the number of lead-in conductors.

I claim:

1. An electron discharge device comprising an envelope, an electrode insaid envelope, at least two lead-in conductors in said envelope, theinner ends of said conductors being short circuited together and to saidelectrode, an electrical resistance heating element spaced from saidinner ends of the conductors and connected across said conductors, and avaporizable getter material on said element.

'2. An electron discharge device comprising an envelope, an electrode insaid envelope, two leadin conductors sealed in the wall of saidenvelope, the inner ends of said conductors being short circuited anddirectly connected to said electrode,

a getter in said envelope comprising metal heating elements connected atits ends to said conductors the points of connection being inter-'mediate the inner ends of the conductors and the lead-in seals of theconductors, and vaporizable getter material on the said member.

3. The method of exhausting an electron discharge device with two leadseffectively short circuited near their inner ends comprising connectinga getter of the resistance heater type across said leads intermediatethe envelope of the device and the short circuited point, and applying atuned high frequency potential to the outer ends of the leads.

4. The method of exhausting an electron discharge device with twolead-in conductors electrically connected together in the device througha path of low ohmic resistance comprising connecting a resistanceheating element carrying getter material across said conductorsintermediate the lead-in seals and the low resistance path, and applyinga high frequency potential to the outer ends of the conductors, saidpotential having such a frequency that the resistance of the circuitincluding said path is greater than the circuit including the heatingelement.

ROLAND B. VANDEGRIFI'.

